1. Field of the Invention
The present invention relates in general to mechanical ventilation, and more specifically to a high-frequency fan ventilators for the treatment of respiratory failure.
2. Description of Related Art
As a result of respiratory failure, it occasionally becomes difficult for particular individuals to breathe without assistance of a respirator or other mechanical apparatus which tends to achieve adequate gas exchange between the blood/lungs and the atmosphere.
A variety of respirators are used to ventilate patients mechanically. Conventional ventilators are operated on a rate of 1-120 cycles/minute (breaths per minute). Such conventional respirators often cause trauma to the airways and to the lungs due to high volume and pressure delivered, and may often fail to provide adequate gas exchange.
To try to solve this problem, methods for high-frequency ventilation have been developed, which use less than physiologic tidal volumes in conjunction with high respiratory rates of 2-30 Hz (120-1,800 rounds or cycles per minute). Several methods and devices for the delivery of high-frequency ventilation have been patented and some of them are used clinically for the ventilation of patients, but with limited success.
U.S. Pat. No. 4,409,977 issued to Bisera, et al, herein incorporated by reference, describes a pump chamber system for high-frequency ventilation operated by a high-frequency inflating/deflating bag located within a closed chamber, thereby defining a pressure compartment between the bag and the chamber's wall. The bag is intermittently compressed by less than 10% of its volume and thus conveys pressure changes into the respiratory system of a patient.
U.S. Pat. No. 5,092,326 issued to Winn, et al, herein incorporated by reference, describes a method for high-frequency oscillatory ventilation using an oscillatory member for back and forth movement, driven by a piston and a cylinder combination, which also control the frequency and amplitude of the oscillatory member.
U.S. Pat. No. 4,838,259 issued to Clark, et al, herein incorporated by reference, describes a multi-frequency jet ventilator and method using a multi-voltage control of solenoid closed valve which helps in periodic interruption of gas flow, thus generating ventilatory pulses.
U.S. Pat. No. 4,351,329 issued to Ellestad, et al, herein incorporated by reference, describes a method for high-frequency breath pump which uses two different selected volumes driven with synchronism of inhalation and exhalation alternatively forcing gas during inspiratory phase and drawing gas during a corresponding expiratory phase.
U.S. Pat. No. 5,165,398 issued to Bird, and which is herein incorporated by reference, describes a high-frequency ventilator using a diaphragm which is associated with a serving chamber and a percussion chamber leading to high-frequency repositioning of the diaphragm from one direction to the center, and then to the other direction.
U.S. Pat. No. 4,788,974 issued to Phuc, and which is herein incorporated by reference, describes a high-frequency artificial respirator using an oscillation generation means connected to patient circuit for imparting high-frequency oscillation, and means for low-pass filtering slowly varying gas components and means for positive pressure generation being interfaced and communicating with means of low-pass filtering.
U.S. Pat. No. 5,271,388 issued to Whitwam et al, describes a ventilator which has a ventilating duct with one end attached to a patient's tube, a gas supply jet extending into the ventilator duct which is rotated about an axis by a motor at a speed corresponding to the required breathing rate, thus producing cyclical flow of gas to and from the patient. However, Whitwam et al uses jet pulses rotated about an axis, rather than a rotating fan or fan's arms.
Thus, it can be seen that high-frequency ventilation modes which have previously been used differ clinically in the following characteristics: (1) frequency of ventilation; (2) ventilatory impulse generation (jet, flow interruption, oscillation); (3) need for conventional ventilatory pressure back-up; (4) port of entry of the ventilatory impulse into the airway; (5) pressure monitoring ports in the ventilation circuit; and (6) pattern of expiration: active or passive.
The main rationale for the use of high-frequency ventilation modes is to minimize barotrauma to lungs and airways caused by high inflation volumes and/or pressures used in conventional respirators, and to try to achieve better gas exchange and alleviate respiratory failure. Therefore, high-frequency ventilation modes use small tidal volumes (equal or less than the dead space volume) with higher than physiological respiratory rates. High-frequency jet ventilation and high-frequency flow interruption have been proven to be effective in treating pulmonary interstitial emphysema, while the use of high-frequency oscillatory ventilation in neonates reduces both the need for extracorporeal membrane oxygenation (ECMO) and to some extent the risk for development of long-term chronic lung disease. However, the above-mentioned three modes do not significantly reduce mortality from respiratory failure.
In addition, the anticipated change in gas exchange and ventilation with the above mentioned high-frequency ventilation modes is questionable, slowly achieved (within hours), and is accompanied by side effects. Those side effects include humidification problems, injury to airway mucosa with life-threatening airway obstruction, systemic air emboli and reduction of venous return to the heart, thus comprising its function and causing hypotension and heart failure. In addition, high-frequency jet ventilation, high-frequency oscillatory ventilation, and high-frequency flow interruption are relatively difficult to handle and very expensive.
Fans have not been used previously for therapeutic mechanical ventilation in humans or animals. While one study used a ventilation fan on a research basis, ventilation fans have not been used for ventilation and gas exchange (Upton CJ, Milner AD, Stokes GM, Carman PGT, "What are the mechanisms producing increased ventilation in dead space studies in neonates?" Pediatr Pulmonol 1990; 9: 136-139.) In this study, hereby incorporated by reference, the effect of adding external dead space tube on minute ventilation and on end-tidal oxygen and carbon dioxide tensions in ventilated infants was examined. The additional tube produced a significant rise in minute ventilation, an effect which was decreased, but not abolished, by the use of a ventilation fan inside the additional tubing.
Furthermore, fans have been widely used to ventilate closed areas at homes, factories or offices and thus lead to exchange of gas. Fans can either ventilate a specific area by forward helical waves (positive pressure) or by backward helical waves (negative pressure), thus sucking gas from a particular area (vacuum). The above characteristics are observed as long as both sides of the fan (in front and behind the fan's arms) are free and not obstructed.
It can be seen then that there is a need for a high-frequency fan ventilator which delivers helical rotatory waves.
It can also be seen that there is a need for a fan ventilator wherein the rotation of the fan causes two distinct types of helical rotating waves for simulating expiration of gas from the lungs while also simulating an active inspiration of gas into the lungs.
It can also be seen that there is a need for a fan ventilator system which includes measurement and monitoring of humidification, temperature and pressure.
Another aspect of the present invention is that an appropriate oxygen mixture is rapidly delivered to the lungs.
It can also be seen that there is a need for a fan ventilator system which avoids causing barotrauma to airway and lungs caused by high ventilatory pressures.